Solar-like oscillations with low amplitude in the CoRoT target HD 181906
R. A. Garcia, C. Regulo, R. Samadi, J. Ballot, C. Barban, O. Benomar, W. J. Chaplin, P. Gaulme, T. Appourchaux, S. Mathur, B. Mosser, T. Toutain, G. A. Verner, … 展开作者
R. A. Garcia, C. Regulo, R. Samadi, J. Ballot, C. Barban, O. Benomar, W. J. Chaplin, P. Gaulme, T. Appourchaux, S. Mathur, B. Mosser, T. Toutain, G. A. Verner, M. Auvergne, A. Baglin, F. Baudin, P. Boumier, H. Bruntt, C. Catala, S. Deheuvels, Y. Elsworth, S. J. Jimenez-Reyes, E. Michel, F. Perez Hernandez, I. W. Roxburgh, D. Salabert
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Paper Accepted to be published in A&A. 10 Pages, 12 figures
Context: The F8 star HD 181906 (effective temperature ~6300K) was observed for 156 days by the CoRoT satellite during the first long run in the centre direction. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (m_v=7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis. Aims: To extract global variables of the star as well as key parameters of the p modes observed in the power spectrum of the lightcurve. Methods: The power spectrum of the lightcurve, a wavelet transform and spot fitting have been used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters have been done by maximizing the likelihood of a global fit, where several modes were fit simultaneously. Results: We have been able to infer the mean surface rotation rate of the star (~4 microHz) with indications of the presence of surface differential rotation, the large separation of the p modes (~87 microHz), and therefore also the ridges corresponding to overtones of the acoustic modes.
Aims. A summary of the CoRoT brown dwarf investigations are presented. Methods. Transiting brown dwarfs around solar like stars were studied by using the photometric time-series of CoRoT, and ground based radial velocity measurements. Results. CoRoT detected three transiting brown dwarfs around F and G dwarf stars. The occurence rate of brown dwarfs was found to be 0.20 +/- 0.15% around solar-like stars which is compatible with the value obtained by Kepler-data.
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A better understanding of the amplitudes of stellar oscillation modes and surface granulation is essential for improving theories of mode physics and the properties of the outer convection zone of solar-like stars. A proper prediction of these amplitudes is also essential for appraising the detectability of solar-like oscillations for asteroseismic analysis. Comparisons with models, or between different photometric missions, are enabled by applying a bolometric correction, which converts mission-specific amplitudes to their corresponding bolometric (full light) values. We derive the bolometric…
Solar analogues are important stars to study for understanding the properties of the Sun. Evolutionary modeling, combined with seismic and spectroscopic analysis, becomes a powerful method to characterize stellar intrinsic parameters, such as mass, radius, metallicity and age.However, these characteristics, relevant for other aspects of astrophysics or exoplanetary system physics for example, are difficult to obtain with a high precision and/or accuracy. The goal of this study is to characterize the two solar analogues HD42618 and HD43587, observed by CoRoT. In particular, we aim to infer prec…
Continuous high-precision photometry of stars, provided by space missions such as CoRoT, Kepler, and K2, represents a unique way to study stellar rotation and magnetism. The coupling of these studies of the surface dynamics with asteroseismology is changing our view to surface and internal dynamics. In this proceedings I will provide the latest developments in the understanding of surface and internal rotation and magnetic fields. I will also discuss the possible discovery of strong internal magnetic fields of dynamo origin in the convective cores of stars above 1.2-1.4 solar masses. I will fi…
Theories of planet formation give contradicting results of how frequent close-in giant planets of intermediate mass stars (IMSs; $\rm 1.3\leq M_{\star}\leq 3.2\,M_{\rm \odot}$) are. Some theories predict a high rate of IMSs with close-in gas giants, while others predict a very low rate. Thus, determining the frequency of close-in giant planets of IMSs is an important test for theories of planet formation. We use the CoRoT survey to determine the absolute frequency of IMSs that harbour at least one close-in giant planet and compare it to that of solar-like stars. The CoRoT transit survey is ide…
So called scaling relations have the potential to reveal the mass and radius of solar-like oscillating stars, based on oscillation frequencies. In derivation of these relations, it is assumed that the first adiabatic exponent at the surface (Gamma_1s) of such stars is constant. However, by constructing interior models for the mass range 0.8-1.6 Msun, we show that Gamma_1s is not constant at stellar surfaces for the effective temperature range with which we deal. Furthermore, the well-known relation between large separation and mean density also depends on Gamma_1s. Such knowledge is the basis …
We estimated blackbody temperature for 209 flares observed at 69 F-K stars, significantly increasing the number of flare temperature determinations. We used the Blue and Red channels obtained by the 27 cm telescope of the CoRoT satellite at high cadence and long duration. The wavelength limits of the channels were estimated using spectra from the Pickles library for the spectral type and luminosity class of each star, provided by the Exodat Database. The temperatures were obtained from the flare energy Blue-to-Red ratio, using the flare equivalent duration and stellar flux in both channels. Th…
We have developed a new automated method intended to perform the simultaneous - and thus more consistent - measurement of both the seismic indices characterizing the oscillations and the parameters characterizing the granulation signature of red-giant stars. This method, called MLEUP, takes advantage of the Maximum Likelihood Estimate (MLE) algorithm combined with the parametrized representation of red giant pulsation spectra following the Universal Pattern (UP). Its performances have been tested on Monte Carlo simulations for observation conditions representative of CoRoT and Kepler data. The…